Pisolithus tinctorius (synonym: Pisolithus arrhizus) is an ectomycorrhizal earthball, sometimes referred to as a dyeball - a reference to one former use for the mature spore mass that this mushroom produces.
Up to 20cm tall, the fruitbodies burst through dry ground and eventually turn into a brown powdery mess that blows away on the wind or gets carried away by rain. Most common in southern Europe but occasionally seen in the UK, these massive fungi have another extremely valuable use: they form mycorrhizal associations with just about any plant that can be grown in soil, and so they are used to produce 'mycorrizal inoculants'. The fungi in effect feed the plants, scavenging vital minerals from the soil via tiny mycelial threads that in effect extend the plant's root system. The fungi also gain nutrients from the plant's photosynthesis process. This is termed a symbiotic relationship.
Here is a picture of the inside of a young specimen of Pisolithus tinctorius:
The spore-producing material looks like rice grains densely packed together. At maturity the appearance is not unlike a pile of rotting horse dung. The one shown below is splitting open and the brown spore mass can be seen:
Foresters use an inoculant made from Pisolithus tinctorius to help young conifers (especially pines) get started on poor or contaminated soil that has lost or perhaps never had the mycorrhizal fungi necessary for trees to survive there.
